The present study aimed at investigating whether previously reported interstrain differences of mice in testicular susceptibility to cadmium toxicity can be attributed to different metallothionein expression in the testes and other organs. Furthermore, purified Leydig cell systems were employed to identify a testicular compartment capable to respond specifically to exogenous cadmium by increased metallothionein expression. It was shown that species differences in testicular damage after cadmium administration can not be explained by differences in cadmium-induced stimulation of hepatic and renal metallothionein. In contrast to these organs, no metallothionein response to cadmium was observed in testicular homogenates. However, both freshly isolated and purified rat Leydig cells and a murine tumor Leydig cell line are not only able to synthesize metallothionein under basal conditions, but also respond to exogenous cadmium by increased synthesis of metallothionein (35S-cysteine incorporation) and an increased Mt-mRNA content. Extracts from freshly isolated and purified rat Leydig cells contained a cadmium-binding component which eluted in gel chromatography with the same properties as metallothionein. It was concluded that the use of purified cell systems is a valuable tool to investigate possible targets of cadmium toxicity.